Scratch Disks and Time Machine - Photoshop error

onlinechris140 said: “Now it's seemingly screwed up this disk. TimeMachine won't backup.”

Does it give a reason? If it does, that would help us troubleshoot it. Does it say it thinks it’s out of space?

With Photoshop quit, what does macOS say the available amount of free space is on the Time Machine drive?

One of the big problems with using a Time Machine drive as a Photoshop scratch disk is that both features are fundamentally about taking over available free space, so that can set them up for a conflict. For example, if you open a Photoshop file so large that you need a lot of scratch disk space (enough that you make Photoshop use the Time Machine drive as a scratch disk), Photoshop might pre-allocate the amount of space it’s going to need. Then, when Time Machine goes to make a backup, it might look at the current free space, reduced by the amount Photoshop has pre-allocated, and say “I don’t have the space to do this.” That’s just a theory because we don’t have more info about why Time Machine is not working.

In theory Time Machine should work fine if you exit Photoshop, because Photoshop is supposed to let go of its scratch disk space when it quits.

"You want at least 25% at all times"
onlinechris140 said: “That's not always possible, this is why I have external SSDs”

When my laptop is out of scratch space, what I do is take a spare external SSD that’s empty, plug it in, and assign that to be the scratch disk. This is a much better solution than plugging in a Time Machine drive, because Time Machine drives are often slow hard drives (it is best for a scratch disk to be fast), and because nothing was competing with Photoshop for the space on the empty external SSD.

In general I try to keep more than 100-150GB of free space on my system drive, and I always spec enough internal storage to make that happen. But when I recently worked on a very large Photoshop document, that wasn’t enough room. I plugged in my external SSD as a scratch drive and found out that particular large Photoshop document wanted to create a 500GB scratch file. In other words, the amount of space you need depends on the size of the Photoshop document, so in some cases you may be opening documents that need more scratch space than the 200GB you are trying to take away from Time Machine. Try to find an empty drive to use as dedicated scratch instead.